Anatomy
Both the iliohypogastric (IH) and ilioinguinal (II) nerves arise from L1 and
emerge from the upper part of the lateral border of the psoas major muscle.
The ilioinguinal nerve is a smaller nerve and courses caudad to the iliohypogastric nerve.

Both nerves cross obliquely anterior to the quadratus lumborum and iliacus muscles
and perforate the transverse abdominis muscle near the anterior part of the iliac crest.
In the anterior abdominal trunk, the nerves travel between the transverse abdominis and
the internal oblique muscles.

Blockade of the II and IH nerves is indicated for analgesia following inguinal
hernia repair because the nerves provide sensory innervation to the skin of the
lower abdominal wall in addition to the upper hip and upper thigh. Because the
lateral cutaneous branch of the IH nerve may pierce the internal and external
oblique muscles immediately above the iliac crest, it is worthwhile to block the
nerves as proximal as possible (i.e., posterior to the anterior superior iliac
spine) before the nerve branches.

Perform a systematic anatomical survey from the iliac crest to the
lower abdomen.

The II and IH nerves are expected to lie within the fascial plane between
the transverse abdominis and internal oblique muscles above the ASIS.

It is important to note that the two nerves may pierce the internal
oblique muscle layer at the ASIS level and travel more superficially
between the internal and external oblique muscles.

Identify the three muscular layers of the abdominal wall: the external
oblique (most external), the internal oblique and transverse
abdominis muscles. The external oblique muscle may be seen only as
a thin layer of aponeurosis.

Ultrasound guided II/IH nerve block is considered an INTERMEDIATE skill
level block. It is challenging is to image the small nerves and
insert the needle in the fascial plane.

In Plane Approach

Insert a 5-8 cm 22 G needle parallel to and inline with the transducer
and the ultrasound beam. It is generally easy to visualize the needle
shaft and tip during needle advancement because this is a
superficial block.

It may be challenging to clearly visualize the needle tip and accurately
place the needle in the fascial plane between the internal oblique
and transverse abdominis muscle layers. Because this plane is a
narrow space, it is worthwhile to inject small amount of fluid
(1-2 mL of saline or local anesthetic) to "hydro dissect" the
appropriate plane.

If the needle is placed inaccurately inside one of the muscle layers,
intramuscular fluid injection is seen during "hydro dissection."

Out of Plane Approach

Coming Soon

Local Anesthetic Injection

Needle placement in the correct plane is indicated by fluid expansion in
a space bounded by the hyperechoic fascial sheath of the internal
oblique and transverse abdominis muscle layers.

A total of 10-20 ml of local anesthetic is injected into this plane.

If only small vessels are visualized in the fascial plane and not the
II/IH nerves, deposit the same volume of local anesthetic around the
vessels in this plane.

Figure A shows hypoechoic nerves within the plane between the internal
oblique muscle (IOM) and the transverse abdominis muscle (TAM).

An ill defined collection of local anesthetic (LA) is seen around the nerves.
The accuracy of injection is questionable resulting in a partial block.

2. Locating A Branch of the Deep Circumflex Iliac Artery

Several hypoechoic structures (arrowheads) may be located within the plane
between the internal oblique muscle (IOM) and the transverse abdominis muscle
(TAM). It is important to use Color Doppler or Color Power Doppler to identify
the branch of the deep circumflex iliac artery (red dot) and not to
inadvertently target the artery.